1. Field of the Invention
The present invention relates to wireless communication, and more particularly, to a method and apparatus for transmitting channel state information in a wireless communication system.
2. Related Art
One of the most important requirements of a next generation wireless communication system is to support a high data rate. For this, various techniques such as multiple input multiple output (MIMO), cooperative multiple point transmission (CoMP), relay, etc., have been under research, but the most fundamental and reliable solution is to increase a bandwidth.
However, a frequency resource is in a saturation state at present, and various schemes are partially used in a wide frequency band. For this reason, in order to ensure a broadband bandwidth to satisfy a required higher data rate, a system is designed such that a basic requirement which allows separate bands to operate respective independent systems is satisfied, and a carrier aggregation (CA) is introduced. In concept, the CA aggregates a plurality of bands into one system. In this case, a band that can be independently managed is defined as a component carrier (CC).
The latest communication standard (e.g., 3GPP LTE-A or 802.16m) considers to expand its bandwidth to 20 MHz or higher. In this case, a wideband is supported by aggregating one or more CCs. For example, if one CC corresponds to a bandwidth of 5 MHz, four carriers are aggregated to support a bandwidth of up to 20 MHz. As such, a system supporting carrier aggregation is called a carrier aggregation system.
Meanwhile, in order to utilize a given channel capacity to the maximum extent possible, a wireless communication system regulates a modulation coding scheme (MCS) and a transmission power according to a given channel by using a link adaptation. In order to perform the link adaptation in a base station, there is a need to feed back channel state information of a user equipment.
According to the conventional technique, when a carrier aggregation system capable of allocating multiple carriers to the user equipment experiences a collision in which periodic channel state information for each of the multiple carriers is simultaneously transmitted in a specific subframe, only periodic channel state information for one carrier determined according to a priority is transmitted. In addition, when the periodic channel state information collides with transmission of acknowledgement/not-acknowledgement (ACK/NACK) for downlink data, the periodic channel state information is not transmitted but is dropped. Therefore, it is difficult to reliably perform periodic channel state reporting.
There is a need for channel state information transmission method and apparatus applicable to the carrier aggregation system.